1. Field of the Invention
This invention relates to a fabrication method for a protective layer. More particularly, the invention relates to a fabrication method for a multi-layered thin film protective layer of a reflective micro liquid crystal display (xcexc-LCD) device.
2. Description of the Related Art
The operation of a reflective micro-LCD device is based on an application of a voltage to the metal layer on the surface of a control circuit. The electric field is generated to control the orientation of the liquid crystal. As light transmits through the liquid crystal and reaches the metal layer, the metal layer reflects the light, which in turn transmits through the liquid crystal. The different orientations of the liquid crystal display different optical properties, thereby displaying in different images on the reflective xcexc-LCD.
During the packaging of the reflective xcexc-LCD device, filling the liquid crystal requires coating a spacer between the glass plate and the device wafer to separate the glass plate and the device wafer. In addition, a protective layer is formed on the metal layer of the device surface to protect the underlying device.
The spacer, however, can only be coated on the periphery of the device, and the glass plate supported by the spacer bends easily at the center of the glass plate due to stress. As a result, while filling the liquid crystal, the thickness of the liquid crystal cannot be uniform. A Newton""s ring thus results. The non-uniform thickness of the liquid crystal seriously affects the quality of the display. Not only the displaying color is changed, but the differentiation between the shades of color is also reduced.
The metal layer of the device requires a protective layer to prevent the metal surface from moisture penetration and from being scratched. The structure of the protective layer and the combination of thicknesses of the thin films directly affect the reflection property of the metal layer. The fabrication of the protective layer is therefore a very critical step in the manufacturing of a reflective micro-LCD device.
In the light of the forgoing, the present invention provides a fabrication for a reflective xcexc-LCD device, wherein protective layers of various structures are formed to satisfy the needs of the different protective layers for the different device areas.
In addition, the present invention provides a fabrication for a protective layer structure as a spacer in the device wafer to support the glass plate and the device wafer and to improve the Newton""s ring effect.
The present invention further provides a fabrication method for a multi-layered thin film protective layer, which is applicable to a substrate comprising a peripheral circuit area and a pixel cell area. A metal layer and pixel cells are formed in the peripheral circuit area and the pixel cell area, respectively, and the metal layers and the pixel cell layers are separated by an insulation material. Thereafter, a first oxide layer, a silicon nitride layer and a second oxide layer are sequentially formed on the pixel cells and the metal layer. The second oxide layer is then defined, which in turn defines the predetermined positions of the pad spacers in the pixel cell area and the peripheral circuit area. The silicon nitride layer and the first oxide layer are further defined to form a first protective layer and to form a pad spacer in the pixel cell area, exposing the pixel cells. After this, a second protective layer is formed on the exposed pixel cells. The pad spacer is formed with a first oxide layer, a silicon nitride layer and a second oxide layer. The first protective layer is formed with the silicon nitride layer and the first oxide layer. The second protective layer is a thin oxide layer.
The present invention accommodates the needs of the different protective layers for the various device areas. A protective layer, which prevents moisture penetration and scratching, is formed to protect the device from being damaged. In the area that requires a high reflectivity, a protective layer with a high reflectivity is formed to fulfill the product requirement. In addition, pad spacers are formed on the device wafer, wherein the pad spacer is higher than the protective layer to facilitate the filling the liquid crystal and to lower the stress generated in packaging, thereby preventing the occurrence of the Newton""s ring effect. The thickness of the liquid crystal is therefore more uniform, and the resulting liquid crystal device has a better capability of differentiating the various shades of color.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.